More Engine Trivia

[GPracer2500]

What four stroke engine from one of the Big Four (Honda, Yamaha, Suzuki, Kawasaki) used intake reeds like those commonly found on two strokes?

Here's a stock reed cage (w/ Boyesen reeds) from a 250r just so there's no question which part I'm talking about:
http://img468.imageshack.us/img468/2419/pb220013hm3.jpg


If you're not sure what the answer is, just guess!! This is just for fun.... :p

[Carter]

81-82 Honda XR500R

[400exrider707]

I went with dozens of four strokes have had them...:o

[GPracer2500]

The answer is the 81-82 Honda XR500R. I consider it a real oddity as it's the only four stroke design I'm aware of that uses intake reeds just like those found on a two stroke.

Item #6 are the reeds and reed cage.
http://i34.photobucket.com/albums/d133/gpracer2500/XR500Rhead.jpg


Here's a view looking into the head at were the reeds go.
http://i34.photobucket.com/albums/d133/gpracer2500/XR500R.jpg
[picture borrowed from "SLIDING"]


This is a 4 valve, rocker operated, single overhead cam design (basically similar to a 400EX). The idea behind using intake reeds in this application was to prevent the carburetor from "double dipping" due to intake reversion at certain RPM.

Intake reversion is when a pulse of pressure actually goes in the reverse direction--up through the intake and carburator. It's caused by the particulars of valve timing events. Intake air picks up fuel as it passes through the carburetor in the normal direction. If that same "fuel loaded" intake air gets pushed back through the carburetor in the opposite direction then it's going to get loaded with fuel again. Carburetors will meter fuel in both directions. They're optimized for metering fuel in only one direction but they will work both ways. So when intake reversion occurs you can wind up with an overly rich mixture--some of the intake air has gone through the carb more than once. This kills throttle response and power.

Part of the problem is that big carburetors weren't as good back then. Getting a carb to work well on great big single cylinder engines was a challenge. Add in some intake reversion and the fueling really gets screwed up. After Honda abandon the 81-82 XR500R cylinder head design they started using dual carb settups (two smaller carbs) for many years. That came with it's own issues and they eventually went back to sinlge carbs on their big singles. But the carbs had gotten better by then as did an understanding of how to mitagate reversion.

Intake reversion of varying degrees is somewhat common in all types of engines (AFAIK). Aggressive cam specifications (or port timing in the case of two strokes) tends to amplify it's strength. It can be a somewhat complicated phenomenon. I'm still trying to learn the ins-and-outs of it all so I'll not try and explain reversion any further--I don't want to get it all wrong and mislead anyone.

Ultimately this idea of intake reeds in a four stroke head didn't pan out for Honda. They used this design on the XR500R for two years before introducing the RVFC (Radial Four Valve Chamber) head that's sill alive and kicking today in the TRX400EX and XR650L.

[JOEX]

Thanks for the lesson, looking forward to more:)

[czrider263]

DSAR

[250r4life]

where did that come from GP? you rebuilding one or something?

[GPracer2500]

Nah. I just stumbled across the fact that the 81-82 XR500R had intake reeds, thought it was weird, and did a little digging about it. When talking to some other folks about this engine a fella WAS rebuilding one and produced that picture.

[Honda#4]

GPracer whats gonna be the next trivia question. I like this trivia that your doing.

[400exrider707]

hmmm a quick google search showed me a hongda generator with a four-stroke motor with intake reeds....

I'll see if I can find it again

notice its a hongda not a honda!

[400exrider707]

Heres a partial report on a study done by SAE with using reed vavles on four strokes...

http://www.sae.org/technical/papers/890222

[400exrider707]

Here's the generator Im talking about, after re-reading, Im still unsure, though it does say "Type: forced air-cooled, four-stroke, reed valve and single-cylinder "

I will try and research this a little more.


Here's the link: http://hongdapower.manufacturer.globalsources.com/si/6008802297211/pdtl/Angle-grinder/1002926838/11.0hp-Four-stroke-Generator.htm

[GPracer2500]

Originally posted by 400exrider707
Heres a partial report on a study done by SAE with using reed vavles on four strokes...

http://www.sae.org/technical/papers/890222

Nice find.

I hate it when I find info I'd really like to see but its only available for a price. :mad:

[GPracer2500]

Originally posted by 400exrider707
Here's the generator Im talking about, after re-reading, Im still unsure, though it does say "Type: forced air-cooled, four-stroke, reed valve and single-cylinder "

I will try and research this a little more.


Here's the link: http://hongdapower.manufacturer.globalsources.com/si/6008802297211/pdtl/Angle-grinder/1002926838/11.0hp-Four-stroke-Generator.htm

The description does seem suspicious. Why would they put such a rare feature on a generator like that? I'm guessing something is being lost in the Chinese-to-English translation.

[NacsMXer]

That's pretty cool, thanks for the read GPracer2500 :cool: I'd love to hear what that XR500R would sound like I could only imagine lol...a thumper with pinger sound :p

[wilkin250r]

Any idea what RPM they were having problems with?

I can imagine a problem at low RPM due to excessive camshaft overlap. I would think the simple solution would be a less aggressive camshaft, but there may have been some reason that wasn't an option.

I can also imagine a problem at higher RPMs due to a combination of intake length and velocity creating a resonance, but that would be within a very narrow range, almost at a single RPM.

There are several different reasons this might occur, most of them at very different RPMs. I'm just curious, the target RPM might clue me in as to which phenomenon was causing the problem.

[GPracer2500]

It was a lower RPM, valve overlap situation. Here's a snippet from the Clymer manual:


REED VALVE ASSEMBLY
XR500
The xr 500r has a power reed valve assembly in the intake port of the cylinder head. The reed valve helps the engine to achieve higher torque in the low to medium engine speed range. On the 4-stroke engine, part of the fuel/air mixture from the carburetor is forced back into the intake port and manifold during low to medium engine speed. This occurs because the fuel/air mixture enters the cylinder at a low velocity and the piston is trying to push it back before the intake valve has closed completely....[pgs. 88 & 89, Clymer #M339]

[400exrider707]

Originally posted by GPracer2500
The description does seem suspicious. Why would they put such a rare feature on a generator like that? I'm guessing something is being lost in the Chinese-to-English translation.

I thought the same thing, but then I thought, what in the world could be mis-translated to that?

I searched and found no more info on this POS. I am tempted to just buy one to tear it apart!

[GPracer2500]

Originally posted by 400exrider707
....I am tempted to just buy one to tear it apart!

:p :p

[Kickstarts-suck]

yea i got it right! I knew it was a honda just couldn't remember what bike so I thought it wouldn't be a goldwing and I was right :D

[54warrior]

Quite Interesting to say the least.